The invention refers to a tubular vascular transplant.
Such transplants are used to connect perfused blood vessels in the human body. The transplant is connected by its first proximal end to a vessel and by its second distal end to another location of the same vessel or a different vessel.
An example is the so called peripheral transplant which is used to bypass a non-perfused blood vessel with the aid of the transplant. Applications within an end-to-side-anastomosis are possible.
Another example of this type of tubular vascular transplant is an arteriovenous shunt. It is a parallel or bypass connection between an artery and a vein, usually in the upper or lower arm to enable operative vascular access during a dialysis. This type of shunt is used when the patient's own veins are inadequately developed to allow for an effective dialysis. Using an arteriovenous shunt, flow rates of up to 1000 milliliters per minute (1000 ml/min) are possible. During a dialysis, a first puncture needle is inserted into the transplant in the proximal area, thus, the area facing the artery. From there the blood will flow through the transplant via a dialysis machine and there it will flow back through a second puncture needle in the distal end of the designated transplant area.
Tubular vascular transplants are usually made of expanded polytetrafluoroethylene and are referred to as an ePTFE-Transplant.
A general problem with such tubular vascular transplants is the formation of a stenosis in the distal region of the transplant. This type of stenosis usually develops within the first six months to two years after the transplant has been carried out. With an arteriovenous shunt the stenosis develops in two areas of the anastomosis: At the base body of the receiving vein an intimal hyperplasia develops near the anastomosis. A pseudointima is formed in the distal end of the transplant.
Similar problems also arise with peripheral transplants or end-to-side-anastomosis.
These chronic changes are to be regarded as a forming phenomena independent from each other. The causes of both phenomena vary according to current scientific findings:                1. Intimal hyperplasia, for example on the base body of the vein with an arteriovenous shunt, is formed due to very high wall shear stress (WSS) in the wall region of the vein which is mainly caused by the angular penetration of the high speed central blood flow.        2 Pseudointimal hyperplasia in the transplant region is formed by dead water zones, so called separation zones, where the blood only flows very slowly or not at all.        
Through the formation of parietal thrombosis a conversion of thrombus occurs in a pseudointima which ultimately leads to luminal narrowing in the transplant. The stenosis is very distinctive here due to widened dead water and vertebration zones in the widened anastomosis region.
The problem with stenosis, in particularly venous stenosis has been well-established for some time. The so called Venaflo®-Transplant has been developed for the arteriovenous shunt (see also EP 1 011 521 B1, in this case in particularly FIGS. 6A and 6B with related description). This European patent specification was also published as DE 696 34 278 T2. This well known transplant is widened by a flange in the distal region which causes a vertebration. The shear stress on the base body of the receiving vessel (i.e.: a vein) is reduced by the vertebrae which prevents a formation of intimal hyperplasia. Various studies show that the stenosis rate is actually less by using this famous Implant in comparison to regular straight end-to-side-transplants. On the other hand however, a distinct pseudointima can form in the distal region when using this famous transplant. This could be due to the development of particularly large vertebration and separation zones in the widening of the transplant.
In the Journal of Vascular Surgery, Volume 37, No. 5, May 2003, as of Page 1032, Albert G. Hakain et al. published a suggestion for the development of an arteriovenous shunt in the venous-side area of the anastomosis.
The straight ePTFE-Prosthesis was connected in such a way in the vein through special incisions, that a diffusion-type flow path was created in the venous area. If in addition the entry angle between the prosthesis and the vein is only small, in particularly around 15 degrees, the blood flow rates can be increased according to those studies. Turbulences are also prevented in this way. Furthermore only a slight stenosis formation showed after 24 months.
Please find below a discussion on the addressed problems of an arteriovenous shunt whereby these problems also occur similarly with peripheral vascular transplants.